For example, a low-temperature plasma spray method, “PlasmaDust”, of company Reinhausen Plasma is known for coating surfaces of substrates. Therein a powder is fed to a low-temperature plasma jet, is partially melted and chemically activated in this plasma jet, and applied by the plasma jet on a surface of a substrate to be coated.
With this technique, it is only possible to achieve line widths of the applied layer not below about 1 millimeter without a mask. Thereby the edges of the lines are not shaped particularly clearly, which is caused by the inhomogeneous density profile of the plasma jet, which is similar to a Gaussian distribution. The usage of masks is laborious and therefore cost-intensive. In particular corresponding masks have to be provided for each desired shape of the layer, even if the number of substrates to be coated is small.
It is known from German patent application DE 10 2008 001 580 A1 to apply the material for a layer as a dispersion of nanoparticles on a surface of a substrate. The nanoparticles applied this way are thermally post-processed by means of a CO2 laser to achieve a desired electric conductivity and transparence of the layer. Regions of the layer, which have not been thermally post-processed, can be removed easily from the surface of the substrate, whereas the regions of the layer, which have been thermally post-processed, adhere very well, compare Zieris R et al., 2003, Characterization of coatings deposited by laser-assisted atmospheric plasma, Materials Park, Ohio: ASM International, pp. 567-572, ISBN: 0-87170-785-3.
High laser power is required for such a thermal post-processing, which can lead to the damage of thermally sensitive substrates.
It is known from the Russian patent application RU 2010 120 868 to illuminate the plasma beam, loaded with powder, by laser light within the plasma nozzle to achieve a better melting of the powder. Since the powder flows through the nozzle after laser irradiation, the laser irradiation does not contribute to the formation of finer structures.
It is known from German patent application DE 10 2007 011 235 A1 to act simultaneously with a laser beam and a plasma jet on a surface. Therein both the laser beam and the plasma jet serve to clean the surface. Coating of the surface by the plasma jet, particularly in cooperation with the laser beam, is not mentioned.
European patent application EP 0 903 423 A2 and German patent DE 197 40 205 B4 describe a method to apply a layer by means of plasma spraying. Thereby at least one continuous laser beam is directed through the spray jet with a given interaction time directly onto the surface of the substrate or the surface of a layer, which has already been applied there, and partially melts it. This method is a high-temperature method using a plasma torch, wherein the high-temperature method is directed at the processing of materials with melting points approximately in the range of 1500-2000° C. The laser beam impinges on the surface of the substrate within the incidence region of the spray jet.
German patent application DE 199 41 563 A1 and German patent application DE 199 41 564 A1 each describe a method for plasma coating using a plasma torch together with a laser. The surface to be coated is locally melted by a laser beam, a plasma beam follows the laser beam and carries the coating material contained in the plasma into the melt. Alternatively the melting with the laser beam can also occur after applying the coating material with the plasma beam.
An overview of the combination of using a laser with a method for plasma spraying can be found in S. E. Nielsen, “Laser fusing—combining laser and plasma spraying techniques for surface improvements”.